1. Field of the Invention
This invention relates to a motor-driven device, and more particularly to an electric dust-proof device for use with a camera, a photographing camera, a projector, or other image formation apparatus to protect a lens thereof from dust.
2. Description of the Related Art
Referring to FIGS. 1 and 2, an electric dust-proof device 1 disclosed in U.S. Pat. No. 5,461,441 is disposed in a housing 10 of a camera for protecting a lens 100 of the camera, and includes a dust-proof plate 11 for selectively covering the lens 100, and a driving unit 12 for driving the dust-proof plate 11 to move between an open position and a close position.
The driving unit 12 includes a motor 120, a driving gear 121 driven by the motor 120 to rotate in two directions, and a gearing consisting of a first gear 122, a second gear 123, a third gear 124, a fourth gear 125, a fifth gear 126, a rack gear 127, and a sixth gear 128. Each adjacent pair of the gears 121, 122, 123, 124, 125, 126, 127, 128 of the gearing meshes with each other. The first, second, third, fourth, fifth, and sixth gears 122, 123, 124, 125, 126, 128 are configured as spur gears.
To rotate the dust-proof plate 11 relative to the lens 100, the motor 120 is operated to rotate the driving gear 121. Rotation of the driving gear 121 is transferred to the first gear 122 by a plurality of interconnected gears (not shown), thereby rotating the second, third, fourth, fifth, and sixth gears 123, 124, 125, 126, 128 and moving the rack gear 127. Hence, the dust-proof plate 11 is rotated between the open position and the close position at a speed slower than that of the driving gear 121.
Although power can be transmitted from the motor 120 to the dust-proof plate 11, a large number of spur gears (i.e., the first, second, third, fourth, fifth, and sixth gears 122, 123, 124, 125, 126, 128) are disposed therebetween for the purpose of speed reduction, thus increasing the manufacturing costs of the electric dust-proof device 1 and the space occupied thereby and resulting in difficulties during assembly thereof.